Surface and catalytic properties of NiO/MgO system doped with Fe2O3

Abstract

The effects of Fe 2 O 3 doping of NiO/MgO system on its surface and catalytic properties were investigated. The amount of NiO was fixed at 16.6 mol% and those of Fe 2 O 3 were varied between 1.03 and 7.69 mol%. Pure and doped solids prepared by wet impregnation method were precalcined at 300–1000 °C. The techniques employed were XRD, nitrogen adsorption at −196 °C, H 2 O 2 decomposition at 30–50 °C and conversion of isopropanol at 200–500 °C. The results revealed that NiO dissolved completely in MgO lattice at temperature ≥ 800 °C forming NiO–MgO solid solution. The doping process conducted at 300 and 500 °C effected a measurable increase in its specific surface area ( S BET ), total pore volume ( V p ) and mean pore radius reaching to maximum limits at certain dopant concentration above which the S BET and V p suffered a sudden decrease. This treatment effected also, a measurable decrease the particle size and degree of ordering of detected MgO phase. A portion of Fe 2 O 3 added to NiO/MgO system conducted at 800–1000 °C interacted readily with the catalyst constituents yielding MgFe 2 O 4 and NiFe 2 O 4 phases. Fe 2 O 3 -treatment conducted at 300 and 500 °C brought about an increase of 442 and 675% in the catalytic activity towards H 2 O 2 decomposition expressed as reaction rate constant per unit surface area ( k − ) measured at 30 °C. The doping process did not modify the mechanism of H 2 O 2 decomposition but rather increased the concentration of active sites contributing in reaction. In isopropanol conversion, pure and variously doped solids behave as dehydrogenation and dehydration catalysts leading to the formation of acetone and propene. The effects of Fe 2 O 3 on the activity and selectivity towards acetone and propene formation were studied and the results showed that the activity and selectivity are dependent on precalcination temperature and dopant concentration.